Abstract: An improved process and apparatus for hydrogenating a stream of hydrocarbons is provided. The pressure and temperature of the stream are elevated and the stream is passed through two or more serially connected hydrogenation reaction zones. While passing through the reaction zones hydrogen is dispersed in the stream and the stream is caused to flow along successive downward and upward paths. The reacted stream is cooled prior to reducing the pressure exerted thereon.

Abstract: A process and apparatus for continuously treating infectious waste, which comprises: (a) introducing bulk unseparated infectious waste material into a receiving container, the receiving container adapted to receive a flow of disinfectant such that the receiving container remains substantially free of infectious contaminants; (b) shredding the waste material by a primary shredder; (c) separating the shredded waste material from waste residue in a separation tank having a predetermined fluid level thereby producing a waste slurry; (d) pumping the waste slurry into a reactor vessel; (e) contacting the waste slurry with a disinfecting fluid in the reactor vessel for a sufficient amount of time to disinfect the waste slurry; and (f) dewatering the disinfected waste slurry to recover solid disinfected waste material.

Abstract: A method of preparing a column for a reaction with distillation process utilizing a solid particulate catalyst includes the steps of providing a plurality of vertically spaced apart distillation devices, coupling these devices with a plurality of vertically extending horizontally spaced catalyst enclosing containers, extending at least some of the containers through at least two successive distillation devices, then loading a particulate catalyst into the containers to form a catalyst bed whereby distillation and catalytic reaction may occur simultaneously in the column. The method also encompasses a process for concurrent catalytic reaction with distillation which includes the foregoing steps as well as the steps of feeding a liquid stream to the column reactor and onto the distillation devices while a vapor stream moves vertically up through the distillation devices while products of reaction and distillation are withdrawn from the reactor.

Abstract: An apparatus for testing performance of a catalyst in a gaseous phase catalytic reaction for a given reactant comprises a reactor receiving a predetermined quantity of fluid reactant discharging the reaction mixture, including reaction products, from the reactor after a predetermined residence time. The reactor comprises a confined reactor volume with an upflow zone and a downflow zone. A device circulates fluids upwardly through the upflow zone and downwardly through the downflow zone where particulate catalysts in the upflow zone are fluidized by the upward flow of the fluid. The circulating device is adapted to circulate the fluid about the reactor volume at a rate which provides at any moment during the residence time for the reactants an essentially uniform concentration of reactants throughout the reactor volume to simulate conditions in a catalytic riser reactor.

Abstract: An ebullated bed reactor into which is introduced a mixture of a gaseous substance, such as hydrogen-rich gases, and a liquid substance, such as vacuum reduced crude or resid, beneath a grid plate disposed in the reactor. Bubble cap risers extend through the grid plate uniformly transmit this gaseous and liquid substance mixture to a catalyst bed disposed above the grid plate. The grid plate is connected to an inner wall of the reactor so that a leakage path might be formed between the grid plate and the support ring of the reactor wall. A skirt is disposed beneath the grid plate to maintain a portion of the gaseous substance in a specific area beneath the grid plate to allow proper distribution of the gaseous flow through the bubble cap riser assemblies. Thus, the portion of the gaseous substance which is maintained beneath the grid plate is prevented from escaping into the reactor via any space which may appear in the grid plate and outside the area which is surrounded by the skirt.

Abstract: The inventive procedure more accurately maintains an inventory of a catalyst in an ebullated bed of a reactor in an oil refinery, especially a resid hydrotreating unit. The ebullated catalyst bed has therein three phases (catalyst, oil, gas). A first density measurement is made of the two-phase mixture in a freeboard zone i.e. in a catalyst free area above the ebullated catalyst. A second density measurement is made in the catalyst bed where all three phases are present. Density measurements are used, along with values for vapor, liquid, and soaked particle densities and corrections for gamma-ray absorption coefficients, to calculate the catalyst particle holdup in the vessel. From this, the amount of catalyst actually in the reactor can be calculated. Once this amount is known, fresh catalyst may be added to or spent catalyst may be removed from the reactor in order to maintain a fixed catalyst inventory within the catalyst bed.

Abstract: A process and apparatus for the batch treatment of infectious waste material in a fluidized bed reactor utilizing gas oxidation, preferably ozone gas diluted in air. The process and apparatus provide for the disinfecting of infectious waste in a rapid, cost efficient manner allowing for disposal of such infectious waste material in an environmentally acceptable manner.

Abstract: A process and apparatus for the batch treatment of infectious waste material in a fluidized bed reactor utilizing gas oxidation, preferably ozone gas diluted in air. The process and apparatus provide for the disinfecting of infectious waste in a rapid, cost efficient manner allowing for disposal of such infectious waste material in an environmentally acceptable manner.

Abstract: In an ebullated bed reactor it has been found that an improved gas-liquid separator effectively removes gas from recycle liquid used to ebullate the catalyst bed. The gas-liquid separator comprises a cup with a plurality of riser conduits. Two stages of cyclone separators effect the final liquid-vapor separation.

Abstract: Apparatus for liquid feed dispersion in fluid catalytic cracking systems is disclosed wherein an improved fluidized catalytic cracking nozzle assembly having a nozzle unit so constructed that substantially all liquid fed through the unit is converted to mist-sized particles over a wide-angle dispersion pattern, the unit being recessed within a protective pipe having a shield on the inside thereof in the area of the recess, without concurrent addition of steam to affect liquid that may flow therethrough.

Abstract: The operation of a fluid-bed reactor in which the catalyst has a proclivity to stickiness deleterious to efficiently carrying out a reaction of the gaseous components fed to the reactor, is controlled by monitoring the fluctuations in temperature at various locations in the bed, and computing the standard deviation of temperature at predetermined intervals of time. When the fluid-bed consists essentially of a supported catalyst performing at peak efficiency, near which it has a proclivity to "stickiness", slight fluctuations, less than 1.degree. F., of operating temperature are correlatable to the quality of fluidization and the risk of an uncontrollable upset in the reactor.

Abstract: Cell culture apparatus comprises a fluidized bed culture tank body in which cell attached porous material is fluidized by air flow, and a pre-culture tank for supplying medium to the fluidized bed culture tank body according to the amount of the liquid medium which is taken out of the fluidized bed culture tank body. By the use of a drain valve which can be controlled to remove liquid medium and porous material or just liquid medium, the cell culture apparatus can continuously produce metabolite.

Abstract: The fluidized bed reactor for biological treatment of effluent essentially comprises a container (1) over the base 2 of which elongated gassing units having gas exit apertures (5) are arranged parallel to one another, in such a way that in each case two neighboring circulating currents (8, 9) in mirror-image symmetry are produced in the reactor. In addition, the reactor (1) is supplied with a retention system (16) arranged on the outside for the separation of carrier particles for biocatalysts suspended in the effluent.

Abstract: A device for injection of a hydrocarbon feedstock into a catalytic cracking reactor comprising, from upstream to downstream in the direction of flow of the feedstock, an intake and mixing system (5) for the liquid hydrocarbon feedstock and steam, a venturi tube (6) whose entrance cone (10) is joined to said intake and mixing system (5), and a protective cap (7) that is integral with the discharge cone (14) of the venturi tube and is provided with an orifice (16) for injection of the feedstock into the reactor. The dimensions of the venturi tube (6) are such that the velocity of the mixture of liquid feedstock and steam attains therein sonic conditions at the level of the throat (13), and the rectilinear throat located between the discharge cone (14) and the entrance cone (10) is connected to such cones continuously by a curved section without making an angle exceeding about 5 degrees and about 15 degrees, respectively, with the axis of the venturi tube.

Abstract: There is disclosed a method for extraction of impurities from a powdery or particulate solid material charged into a extractor. According to the disclosure, not only can the extraction of impurities be carried out efficiently, but also the refinement of a solid material can be carried out, with the degree of the extraction of the impurities being very high.

Abstract: A semi-continuous multi-stage catalytic reactor system for converting lower olefinic feedstock to heavier liquid hydrocarbon product.

Abstract: The liquid feed injector as hereindescribed uses sequential stages of increased severity mixing to fully atomize a liquid portion of a combined liquid and gaseous stream. Sequential mixing consists of a first mild mixing that takes place in a mild mixing zone and blends the liquid and gaseous material into a substantial uniform mixture. The uniform mixture of liquid and gaseous material passes through another stage of vigorous mixing where the liquid is sheared and gas is dispersed throughout the liquid by dividing the mixture into a plurality of small streams and directing the projection of the streams into impingement with an impact medium to produce a homogeneous mixture of fine gas bubbles dispersed in the liquid. The homogeneous liquid and gas mixtures are then discharged through one or more discharge nozzles to effect atomization and distribution of the liquid in a suspension of fluidized solids.

Abstract: A method and apparatus for exposing particles to a fluid including the steps of adding fluid and particles to a container having impeller means therein, generating a current with the impeller so as to subject the particles to centrifugal and convective forces resulting in the formation of a well-defined and localized fluidized bed of particles, and maintaining the existence of the current through the fluidized bed so that the particles are thereby exposed to the fluid. The fluidized bed is located in a region removed from the impeller when the particles are more dense than the fluid, and the fluidized bed is located in a region near the impeller when the particles are less dense than the fluid. A method of exposing a first fluid to a second fluid, the second fluid being either a gas or a liquid immiscible in the first fluid is also disclosed.

Abstract: Crystalline silicon ingots are produced directly from an internally heated bed of silicon particles.

Abstract: Heat transfer equipment is provided having a chamber adapted to contain a bed of free-flowing granular material and a plurality of spirally wound cylindrical tube coils nested together which extend concentrically around a centrally positioned tube collector. Each tube coil is wound on a cylindrical surface having an axis coinciding with the longitudinal axis of the chamber. The tubes at least at the top end of the chamber emerge from the coil and remain on the cylindrical surface as they extend in a direction substantially parallel to the longitudinal axis. The tubes then bend about 90.degree. and extend radially toward the longitudinal axis and connect to the centrally positioned tube collector. In the radial run, the tubes from different tube coils overlap one another on the top of the coils and extend radially over substantially the same outer surface of the tube coils. A retaining device adapted to be removed in sections is positioned below the tubes in the chamber.

Abstract: A process and system for low-temperature carbonization of oil shale, oil sands and similar oil-bearing solids includes low-temperature carbonization of oil-bearing solids in a high-pressure fluidized bed reactor in the presence of a substance selected from the group consisting of hydrogen and steam at temperatures substantially between 400.degree.and 600.degree. C. for producing low-temperature carbonization gas. The low-temperature carbonization gas is condensed in at least two stages for producing relatively higher boiling and relatively lower boiling oil fractions. The oil-bearing solids are peripherally mashed with the higher boiling oil fraction of the low-temperature carbonization gas, before introducing the oil-bearing solids into the high-pressure fluidized bed reactor. The oil-bearing solids mashed with the higher boiling oil fraction are returned to the high-pressure fluidized bed reactor.

Abstract: A fluid catalytic cracking (FCC) process and apparatus which employs relatively more elutriatable catalyst particles comprising intermediate pore zeolite, particularly ZSM-5, and relatively less elutriatable catalyst particles comprising large pore zeolite, preferably zeolite Y. The process and apparatus employ a first stripping vessel which also separates a more elutriatable first portion of catalyst from a less elutriatable second portion of catalyst. The more elutriatable first portion passes to a second stripping vessel, and subsequently recycles to a fluid catalytic cracking reactor riser. The second portion of less elutriatable catalyst passes from the first stripping vessel to a fluid catalytic cracking regenerator vessel and, after being regenerated, recycles to the reactor riser. The more elutriatable first portion contains a higher ratio of intermediate pore catalyst particles to large pore catalyst particles than does the second portion.

Abstract: The invention concerns an apparatus comprising (FIG. 3):a substantially vertical reactor (1),means (2) for introducing solid particles into the upper part of the reactor,means (4) for withdrawing solid particles from the lower part of the reactor,at least one funnel defining a flared zone (25), whose apex is turned downwardly, andmeans (7 and 8) for introducing a fluid charge, formed of a liquid and a gas, into the lower part of the reactor under the funnel (25).The apparatus is characterized by the presence of a charge injection device, comprising:at least one substantially vertical leg or pipe (24) passing through the funnel, anda cap (26) covering the upper end of pipe (24), the lower part (or fringe) of the cap comprising several indentations or a series of indentations arranged over the major part of its perimeter.

Abstract: In an alkylation process wherein the amount of hydrogen fluoride (HF) acid catalyst required to maintain a desired HF acid/hydrocarbon ratio in a plurality of alkylation reactors is contained in the lower portion of a common settler vessel, the improvement comprises: dividing the lower portion of the common settler vessel into a plurality of chambers for containing the desired amount of HF acid catalyst, such that a leak affecting the catalyst handling system for one of the plurality of reactors would only spill the amount of liquid HF acid contained in one of the chambers, and would not affect the liquid HF acid level in a non-leaking chamber.

Abstract: An improved liquid hydrocarbon feed method is disclosed wherein substantially all of the liquid is converted to mist sized particles over a wide angled dispersion pattern without a concurrent shroud of steam or water. Such dispersion promotes vapor phase catalytic reaction between hydrocarbon vapors and fluidized catalyst in a reaction time of 1 to 3 seconds. The misting nozzle is characterized by a swirl chamber to which the full hydrocarbon feed, with or without steam included in the feed, is supplied for centrifugal rotation by vane members to form a free vortex. The flow is then released through a reduced area square-edge orifice having a short throat to form and maintain a characteristic "vena contrata" from such an orifice during flow into the catalyst stream in the riser reactor for dispersion over a wide angled conical dispersion pattern. Such flow from the orifice allows the nozzle to be recessed out of the flowing catalyst stream.

Abstract: A new process for continuously preparing granules having narrow grain size distribution, comprisinga. spraying the product to be granulated in liquid form into a fluidized bed,b. separating the proportions of fine material escaping from the fluidized bed from the off-gas and returning said fine material to the fluidized bed as nuclei for granule formation,c. setting the fluidizing gas flow such that granules are formed which are of a predetermined size, andd. removing the completed granules solely by way of at least one countercurrent gravity classifier inserted into the outflow bottom of the fluidized-bed vessel.A new apparatus for carrying out the process according to the invention and new granules.

Abstract: Particulate material is discharged continuously from fluidized bed reactors by passing the material emerging at the lowest point of the fluidized bed through a zone which is narrower than the fluidized bed and in which a gas stream flows counter-current to the material, the pressure of the gas stream being above the pressure of the fluidized zone.

Abstract: Apparatus for the treatment of a liquid hydrocarbon charge containing solids or solids-forming contaminants, e.g., inorganic solids, metals and asphaltenes, which includes a contactor vessel having a liquid charge inlet, a vaporizing media inlet above the charge inlet and a vapor-solids outlet. An atomizer is positioned in the charge inlet for forming small particles of the liquid charge and directing the particles of liquid in a substantially horizontal flat pattern into the contactor vessel. A premix downcomer having a dispersion grid positioned therein is located in the vaporizing media inlet for introducing a fluidized mixture of a gas dispersion media and hot circulating solid particles into the contactor vessel in a substantially vertical flat pattern to traverse the path of the liquid particles and intimately contact the liquid particles.

Abstract: Apparatus for treating particles while the particles are suspending in a circulating stream of air or other fluid. The apparatus causes particles to rotate around a vertical axis in confined circular paths of travel generally lying in a horizontal plane.

Abstract: A succession of low profile catalyst chambers each housing a reservoir of catalyst are alternately connected in sequence by openings below the levels of the catalyst reservoirs and openings thereabove. The catalyst in all reservoirs is fluidized by a gas moving upwardly therethrough. Separate portions of the sequence of chambers are operated as reactor and regenerator sections according to the gas used to fluidize the catalyst in those sections. Other portions of the sequence of chambers are used to create inert atmospheric seals between the reactor and regenerator sections. The entire apparatus is configured as a low-profile catalytic cracker wherein the fluidized flow of the catalyst moves throughout the apparatus in an alternating lifting and dropping sequence.

Abstract: New processes and equipment are disclosed for producing elemental phosphorus and thermal phosphoric acid. Benefits are listed below.1. Phosphorus-containing solids are recycled to smelting furnaces thus eliminating hazardous waste generation.2. Phosphorus furnace feedstock is upgraded and this permits unbeneficiated phosphate ore to be smelted.3. Energy is conserved during manufacture of elemental phosphorus and phosphoric acid.4. Electric energy is produced by cogeneration.5. Fluorine in phosphate ore is recovered as ammonium fluoride.6. Phosphorus-containing liquids are used as feedstock for production of suspension fertilizers.Benefits are achieved by agglomerating phosphate ore with monocalcium phosphate binder by a method which upgrades the ore. Phosphorus-containing solids are fluidized and burned to form an impure phosphoric acid mixture which is reacted with small sized phosphate ore to form monocalcium phosphate binder.

Abstract: A floating recycle pan is provided to control the flow of the feed into and out of the downcomer even while the oil liquid level in the ebullated bed reactor is varied to provide continuous ebullation and enhance the efficiency and yield of the process.

Abstract: Disclosed is a method for the production of benzene carboxylic acids and benzene carboxylic acid esters or their mixtures, while p-toloylic acid is made from p-xylene and terephthalic acid monomethyl ester is simultaneously prepared from p-toluylic acid ester. The oxidation is performed by the addition of oxidator liquid and gases containing oxygen in single orifice mixing nozzles with the formation of a highly disperse reaction phase and the single orifice mixing nozzles open into the oxidator liquid.

Abstract: In an ebullated bed reactor it has been found that an improved gas-liquid separator effectively removes gas from recycle liquid used to ebullate the catalyst bed. The gas-liquid separator comprises a cup with a plurality of riser conduits. Helical members are positioned within the riser conduits which impart a tangential velocity component to the fluid. Cyclone separators effect the final liquid-vapor separation. Vapor is directed to a vapor rich zone in the reactor.

Abstract: A wheel-like apparatus for the generation of whirling flow and a fluidized bed under zero gravity conditions having spokes which contain at least one reaction chamber for solid particles. Gas is fed into the chamber in radial inward direction for fluidizing action of the particles against any centrifugal force while liquid is sprayed into the chamber radially inwardly or outwardly. Gas plus vaporized liquid is extracted from the chamber in radial inner points and the gas is circulated back after separating the vapor from the gas.

Abstract: A process is disclosed for the catalytic cracking of hydrocarbons in a fluidized bed wherein the catalyst particles are injected in a fully fluidized suspension into an elongate reaction zone. In accordance with the process, the feedstock to be cracked is injected in a state of small droplets less than 200 microns in diameter countercurrently to the flow of the fully fluidized suspension of catalyst particles.

Abstract: A bubble cap assembly and distributor plate is revealed uniquely suited for a reactor in an ebullated bed process. In the riser of the bubble cap assembly a ball check valve is mounted on a valve seat. An orifice mixer below the valve seat delivers a homogeneous vapor-liquid mixture to the orifice in the valve seat thereby minimizing slug flow which causes destructive valve chatter. The fluid outlet port is positioned in the riser to hydraulically limit ball travel between the valve seat and the cap, eliminating the need for pins or other restraints.

Abstract: Process and apparatus for catalytic conversion of oils. A furnace heats a feedstock which is provided to a separator for separation of the feedstock into a gas vapor phase and a liquid phase. The liquid phase is provided under pressure to a venturi nozzle which atomizes the liquid oil. The atomized oil and the gas are each provided to a reactor such as the lower end of a riser reactor in a fluid catalytic cracking unit.

Abstract: FCC catalyst is regenerated in a process providing increased coke-burning capacity without additional heat evolution or air consumption. The process uses a two-stage regeneration arrangement providing initial coke combustion in a low catalyst density-high efficiency contact zone followed by substantial separation of catalyst and regeneration gas and complete regeneration of catalyst particles in a dense bed regeneration zone. Catalyst and gas flow cocurrent prior to this separation but flow countercurrent after the separation. An effective control scheme for regulating oxygen addition to the final zone is also disclosed. This process is applicable to FCC operations for conventional and residual feedstocks.

Abstract: Apparatus for altering the physical properties of particles while the particles are suspended in a circulating stream of air or other fluid. The apparatus includes a mechanism for mechanically forming a vortex in a volume of gas, a mechanism for introducing particles into the vortex, and, particle treatment apparatus generally adjacent the vortex for altering at least one of the physical properties of the particles in the vortex.

Abstract: The present invention relates to a process for immediately and intimately mixing a fluidizable cracking catalyst with a fluid hydrocarbon in a riser reactor. The process involves passing the hydrocarbon through a stationary fluid feedstock feed means in fixed relationship with the upstream end of the riser. The feedstock is atomized by a nozzle attached to the downstream end of the feed means. A hollow plug valve positioned concentrically around the feed means is capable of moving in a reciprocating fashion to permit the flow of catalyst to the riser.

Abstract: A method and apparatus for feeding catalyst, oil and steam into a fluid catalytic cracking (FCC) riser. Oil passes through respective oil lines into a multiplicity of upwardly extending nozzles located at a lower portion of the riser, while steam passes through respective steam lines into the nozzles where it blends with the oil, with the combined oil and steam mixture being fed through the nozzles into the riser. Each oil line and steam line is provided with a valve to separately control oil and steam flow rates, respectively, in each of the nozzles to obtain a substantially constant catalyst to oil ratio across a horizontal cross-section of the riser. The substantially constant catalyst to oil ratio is represented by a substantially isothermal temperature profile across the horizontal riser cross-section, which is detected by measuring the temperature at various points along the horizontal cross-section.

Abstract: The present invention relates to a process for immediately and intimately mixing a fluidizable cracking catalyst with a fluid hydrocarbon in a riser reactor. The process involves passing the hydrocarbon through a hollow plug valve engageable with the upstream end of a riser reactor. The hydrocarbon is atomized by a nozzle attached to the downstream end of the hollow plug valve. The plug valve is capable of moving in a reciprocating fashion to permit the flow of catalyst to the riser.

Abstract: A process for reacting substrates with biocatalysts in a two-phase liquid system disposed in a columnar vessel having a top portion with an exit opening and a first filter disposed therein, a bottom portion with an entrance opening and a second filter disposed therein, a feed line connecting the exit and entrance openings, and a pump disposed in the feed line. The process comprises the steps of: stirring the two-phase liquid in the columnar vessel to accelerate sedimentation and minimize accumulation of the biocatalysts in the top portion of the vessel; selectively controlling the temperature of the two-phase liquid within the vessel; drawing, with the pump, a portion of the two-phase liquid through the exit opening and first filter; and passing the drawn-off portion of the two-phase liquid through the feed line and through the entrance opening and second filter into the vessel to enhance miscibility of the individual phases of the two-phase liquid with the vessel.

Abstract: A vapor collector and process utilizes a skirted pan to collect vapor in an ebullated bed reactor and substantially minimize gas entrainment so as to enhance the efficiency and yield of resid hydrotreating.

Abstract: A method for accelerating the transfer of media between materials reacting in a fluidized bed in a centrifuge. The rotating fluidized bed increases the relative boundary layer velocities of the phases and assists in the transfer of material across the interface.

Abstract: A mixing chamber for catalyst and oil in a catalytic cracking unit in which atomized oil is introduced preferably axially in a preferably vertically oriented transfer line or riser reactor from an atomization chamber segregated from flow of cracking catalyst. The cracking catalyst flows with a radially inward component to the mouth of the riser from the circumference thereof and mixes with the oil feed.

Abstract: An improved liquid hydrocarbon feed method is disclosed wherein substantially all of the liquid is converted to mist sized particles over a wide angled dispersion pattern without a concurrent shroud of steam or water. Such dispersion promotes vapor phase catalytic reaction between hydrocarbon vapors and fluidized catalyst in a reaction time of 1 to 3 seconds. The misting nozzle is characterized by a swirl chamber to which the full hydrocarbon feed, with or without steam included in the feed, is supplied for centrifugal rotation by vane members to form a free vortex. The flow is then released through a reduced area square-edge orifice having a short throat to form and maintain a characteristic "vena contrata" from such an orifice during flow into the catalyst stream in the riser reactor for dispersion over a wide angled conical dispersion pattern. Such flow from the orifice allows the nozzle to be recessed out of the flowing catalyst stream.

Abstract: A floating recycle pan and ebullated bed process are provided to control the flow of the feed into and out of the downcomer even while the oil liquid level in the ebullated bed reactor is varied to provide continuous ebullation and enhance the efficiency and yield of the process.

Abstract: An apparatus for catalyst/oil mixing in a catalytic cracking unit comprises a bifluid nozzle for atomizing oil having an outer tube with an end connected to the sidewalls of a coaxial inner tube forming an annulus therebetween, and apertures through the inner tube for mixing steam introduced into the annulus with oil introduced into the inner tube. The inner tube has an end protruding past the end of the outer tube with a cap having a slot affixed to the end of the inner tube, and a plate baffle mounted inside the inner tube and extending partially thereacross near the apertures. The apparatus further comprises a means for providing a flow of cracking catalyst particles along an exterior surface of the cap so as to sweep the length of the slot.